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ALPO Comet News for September 2024

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#1 Carl H.

Carl H.

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Posted 31 August 2024 - 04:14 PM

ALPO COMET NEWS FOR SEPTEMBER 2024
A Publication of the Comets Section of the Association of Lunar and Planetary Observers
By Carl Hergenrother

 

The monthly Association of Lunar and Planetary Observers (ALPO) Comet News PDF can be found on the ALPO Comets Section website @ http://alpo-astr....org/Comets/ and in the Comets Section Image Gallery. A shorter version of this report is posted here (minus the magnitude estimates, images, and other figures contained in the full PDF). The ALPO Comets Section welcomes all comet-related observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. You do not have to be a member of ALPO to submit material, though membership is encouraged. To learn more about the ALPO, please visit us @ http://alpo-astronomy.org. We can also be reached at < comets @ alpo-astronomy.org >.

 

Summary

 

The stage is set for C/2023 A3 (Tsuchinshan-ATLAS), which will arrive at the perihelion on September 27. In August, the comet continued to slowly brighten, but otherwise, it looked healthy. The STEREO-A spacecraft took the last observations on August 21, with the comet now too close to the Sun to be observed.

 

Assuming the comet continues to brighten and not disintegrate, it should become observable again during the second half of September, at least for those clear, unobstructed eastern morning horizons. The comet will be competing with a rapidly brightening dawn sky. It should be within range of imagers, but will it be bright enough for visual observations?

 

The real show will be in October, when the comet may become a short-lived daylight comet from October 8 to 10 and then a nice evening object starting around October 13.

 

Two other comets are expected to be brighter than 12th magnitude in September. 13P/Olbers is a northern hemisphere object fading from 8th to 9th magnitude in the evening sky. 12P/Pons-Brooks is a southern hemisphere object fading from 10-11th magnitude, also in the evening sky.

 

Last month, the ALPO Comets Section received 103 images and 167 magnitude estimates of 22 comets: C/2023 V4 (Camarasa-Duszanowicz), C/2023 C2 (ATLAS), C/2023 A3 (Tsuchinshan-ATLAS), C/2022 N2 (PANSTARRS), C/2021 S3 (PANSTARRS), C/2021 G2 (ATLAS), C/2020 V2 (ZTF), C/2020 K1 (PANSTARRS), P/2010 WK (LINEAR), 328P/LONEOS-Tucker, 305P/Skiff, 302P/Lemmon-PANSTARRS, 146P/Shoemaker-Levy, 136P/Mueller, 133P/Elst-Pizarro, 130P/McNaught-Hughes, 125P/Spacewatch, 89P/Russell, 54P/de Vico-Swift-NEAT, 37P/Forbes, 13P/Olbers, and 12P/Pons-Brooks.

 

A big thanks to our recent contributors: Dan Bartlett, José J. Chambó, Michel Deconinck, Jose Guilherme de Souza Aguiar, Juan Jose Gonzalez Suarez, Christian Harder, Eliot Herman, Michael Jäger, John Maikner, Gianluca Masi, Michael Mattiazzo, Martin Mobberley, Mike Olason, Andrew Pearce, Chris Schur, and Christopher Wyatt.

 

Request for Observations

 

As always, the Comet Section is happy to receive all comet observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. Please send your observations via email to the Comets Section < comets @ alpo-astronomy . org >, Comets Section Coordinator Carl Hergenrother < carl.hergenrother @ alpo-astronomy . org > and/or Comets Section Acting Assistant Coordinator Michel Deconinck < michel.deconinck @ alpo-astronomy . org >.

 

Photometric Corrections to Magnitude Measurements

 

We include lightcurves for the comets discussed in these reports and apply aperture and personal corrections to the visual observations and only personal corrections to digital observations. Though we try to keep these lightcurves up to date, observations submitted in the days before publication may not be included in the lightcurves until next month’s News. All magnitude estimates are affected by many factors, including instrumental (aperture, focal length, magnification, type of optics), environmental (sky brightness due to moonlight, light pollution, twilight, aurora activity, zodiacal light, etc.), cometary (degree of condensation, coma color, strength and type of gas emission lines, coma-tail interface) and personal (sensitivity to different wavelengths, personal technique, observational biases). The first correction used here corrects for differences in aperture [Charles S. Morris, On Aperture Corrections for Comet Magnitude Estimates. Publ Astron Soc Pac 85, 470, 1973]. Visual observations are corrected to a standard aperture of 6.78 cm by 0.019 magnitudes per centimeter for reflectors and 0.066 magnitudes per centimeter for refractors. After applying the aperture correction and if a sufficient number of visual observations are submitted for a particular comet, we also determine personal corrections for each observer for each comet; for digital observations, only a personal correction is applied. A single observer submitting both visual and digital magnitude measurements may also have separate corrections for each observing method. If the magnitudes shown in the text don’t match those plotted in the lightcurves, it is because of the application of these corrections.

 

Acknowledgments

 

In addition to observations submitted directly to the ALPO, we occasionally use data from other sources to augment our analysis. Therefore, we acknowledge with thanks observations submitted directly to the ALPO and those submitted initially to the International Comet Quarterly, Minor Planet Center, and COBS Comet Observation Database. In particular, we have been using observations submitted to the COBS site by Thomas Lehmann for our analysis and would like to thank Thomas for his COBS observations. We would also like to thank the Jet Propulsion Laboratory for making their Small-Body Browser and Orbit Visualizer available and Seiichi Yoshida for his Comets for Windows programs that produced the lightcurves and orbit diagrams in these pages. Last but not least, we’d like to thank Syuichi Nakano and the Minor Planet Center for their comet orbit elements, the asteroid surveys and dedicated comet hunters for their discoveries, and all of the observers who volunteer their time to add to our knowledge of these fantastic objects.

 

Thank you to everyone who contributed to the ALPO Comets Section!

 

Clear skies!
- Carl Hergenrother

 

Comets Calendar

 

Lunar Phases (UTC)

 

Sep 03 - New Moon
Sep 11 - First Quarter Moon
Sep 18 - Full Moon
Sep 24 - Last Quarter Moon

 

Comets at Perihelion

 

Sep 03 - 54P/de Vico-Swift-NEAT [q = 2.17 au, 7.4-yr period, V ~ 18, visual discovery by de Vico in 1844 (q = 1.19 au), visual re-discovery by Swift in 1894 (q = 1.39 au), photographic recovery by Klemola in 1965 (q = 1.62 au), CCD re-discovery by NEAT in 2002 (q = 2.14 au), also seen at 2009 return, missed at 2017 return, seen at 6 returns and missed at 23 returns since discovery]
Sep 06 - P/2014 MG4 = 2024 K2 (Spacewatch-PANSTARRS) [q = 3.72 au, 11.2-yr period, V ~ 19-20, discovered in 2014, 2024 is 2nd observed return]
Sep 06 - C/2024 G5 (Leonard) [q = 2.95 au, V ~ 19]
Sep 09 - C/2021 G2 (ATLAS) [q = 4.98 au, V ~ 13-14]
Sep 14 - C/2022 E2 (ATLAS) [q = 3.67 au, V ~ 11-12]
Sep 16 - C/2023 TD22 (Lemmon) [q = 2.36 au, V ~ 16]
Sep 19 - 384P/Kowalski [q = 1.11 au, 4.9-yr period, V ~ 18, discovered in 2014, seen at 2019 return, 3 observed returns]
Sep 27 - C/2023 A3 (Tsuchinshan-ATLAS) [q = 0.39 au, see much more below]
Sep 28 - P/2019 M2 = 2024 C6 (ATLAS) [q = 1.07 au, 5.3-yr period, V ~ 20, discovered in 2019, passed 1.06 au from Earth in 2019, the current return is similar with an approach to 1.07 au of Earth, low activity short-period comet observed at 2 returns]

 

Photo Opportunities

 

Sep 01    - 13P/Olbers within a degree or so of the bright globular cluster pair M53 and NGC 5053
Sep 22-23 - 12P/Pons-Brooks passes over the bright Omega Centauri (NGC 5139) globular cluster!
Sep 30    - 13P/Olbers passes within 20’ of 10th mag galaxy NGC 5701

 

Comets News

 

Looking Ahead to the Next 12 Months

The chart below shows those comets expected to become brighter than magnitude 10 in 2024. The number in each date bin is the expected brightness for that date. Magnitudes are only shown for dates when the comet is above the horizon during the dark of night (between the end of astronomical twilight in the evening and the start of astronomical twilight in the morning). The only exceptions are the dates bolded in red for C/2023 A3 (Tsuchinshan-ATLAS) and C/2024 G3 (ATLAS), when the comets will only be above the horizon in bright twilight but may still be bright enough to be observed.

 

All brightness predictions are just that—predictions and may be off by many magnitudes.

 

Comet Observability.jpg

 

Last 10 Periodic Comet Numberings (from WGSBN Bull. 4, #11)

 

486P/2018 L5 = P/2024 H1 (Leonard)                            MPC 174198
485P/2022 U6 = P/2006 AH2 (Sheppard-Tholen)                   MPC 172941
484P/2005 XR132 (Spacewatch)                                  MPC 172941
483P/2016 J1 = P/2010 M9 = P/2020 Y6 = P/2021 K5 (PANSTARRS)  MPC 171409
482P/2014 VF40 (PANSTARRS)                                    MPC 171409
481P/2012 WA_34 = P/2024 C5 (Lemmon-PANSTARRS)                MPC 171409
480P/2014 A3   = P/2023 X6 (PANSTARRS)                        MPC 169139
479P/2011 NO1  = P/2023 WM26 (Elenin)                         MPC 169139
478P/2023 Y3   = P/2017 BQ100 (ATLAS)                         MPC 169139
477P/2018 P3   = P/2023 V8 (PANSTARRS)                        MPC 169139

 

New Recoveries & Discoveries

 

P/2024 Q1 (PANSTARRS) - The Pan-STARRS asteroid survey found this 20th magnitude comet on 2024 August 27 with one of their 1.8-m reflectors at Haleakala. P/2024 Q1 is a short-period comet with a 6.6-year orbital period. Perihelion was on 2024 June 14, at 1.64 au. The comet is now fading. [CBET 5437, MPEC 2024-Q87]

 

P/2024 O3 = P/2010 WK = P/2010 PB_57 (LINEAR) – The "Zwicky Transient Facility" (ZTF) picked up an apparently asteroidal object in July and August at 19th magnitude. The object was identified as the returning short-period comet P/2010 WK (LINEAR). It was also linked with the apparent asteroid 2010 PB57. Perihelion was on 2024 July 20, at 1.78 au. Currently, P/2024 O3 is roughly 3 magnitudes fainter in absolute brightness than it was in 2010. With perihelion in July, the comet should now fade. With a 13-year orbital period, it’ll return to perihelion in April 2038. [CBET 5436, MPEC 2024-Q34]

 

P/2024 O2 (PANSTARRS) – The Pan-STARRS1 1.8-m reflector at Haleakala discovered a 20-21st magnitude short-period comet on 2024 July 28. Pan-STARRS pre-discovery observations were found from 2024 June 30. P/2024 O2 should now fade after its 2024 April 19 perihelion at 3.70 au. The comet has a 20-year orbital period. [CBET 5428, MPEC 2024-P90]

 

P/2024 N6 = P/2002 QU151 (NEAT-PANSTARRS) – This short-period comet was discovered in 2012 by amateur astronomer Reinder J. Bouma in archival NEAT observations from 2002. Since the object’s cometary appearance was “borderline” in the 3 nights of observations from 2002, it wasn’t designated as a comet but rather as an asteroid, 2002 QU151. The Pan-STARRS survey serendipitously re-discovered the object as a comet on 2024 July 9 at 20th magnitude with their Pan-STARRS2 1.8-m reflector at Haleakala. Like the previous two discoveries above, P/2024 N6 has passed its perihelion and fading [T = 2024 May 19 at 1.68 au]. With a 7-year orbital period, its next perihelion will be in December 2031. [CBET 5427, MPEC 2024-P41]

 

P/2024 K2 = P/2014 MG4 (Spacewatch-PANSTARRS) – Rob Weryk reported the recovery of P/2014 MG4 (Spacewatch-PANSTARRS) by the Pan-STARRS1 1.8-m in April and May 2024 images at 21st magnitude. Perihelion will be on 2024 September 6, at 3.72 au, with the comet peaking at 20th magnitude next July. S. Nakano reports in CBET 5431 that the comet passed 0.05 au from Jupiter in 1955. Before close approach with Jupiter, the comet was on a 44.8-year orbit with a perihelion at 5.29 au. The comet’s current orbit has an orbital period of 11.2 years. [CBET 5431, MPEC 2024-Q26]

 

P/2024 C6 = P/2019 M2 (ATLAS) - Rob Weryk also reported the recovery of P/2019 M2 (ATLAS) on images taken by the Pan-STARRS1 and 2 telescopes in February, March, and April of 2024. Though it has a relatively small perihelion distance of 1.07 au (on 2024 September 28), it also appears to be a very low-activity comet and is not expected to become brighter than 20th magnitude. In 2019, it approached to 0.21 au of the Earth but never got brighter than 17-18th magnitude and displayed a very weak coma and tail. With a 5.3-year orbital period, it will be next at perihelion in January 2030. [CBET 5433, MPEC 2024-Q25]

 

C/2023 TD22 (Lemmon) – The Mount Lemmon Survey used their 1.5-m telescope to discover this apparently asteroidal object on 2023 October 12 at 20th magnitude. Recent observations have found cometary activity resulting in its redesignation as a comet. C/2023 TD22 (Lemmon) is a long-period comet with an orbital period of 334 years. It is currently peaking at 16th magnitude as it approaches a 2024 September 16 perihelion at 2.36 au. [CBET 5429, MPEC 2024-P107]

 

P/2023 JN16 (Lemmon) – Another apparently asteroidal Mount Lemmon discovery from 2023 has been observed to be active. Discovered on 2023 May 10 at 19th magnitude, P/2023 JN16 is a Main Belt comet or activated asteroid. The recognition of P/2023 JN16 as a comet resulted from a collaboration due to the effort of amateur astronomers on the Minor Planet Mailing List.

 

On June 1, Peter VanWylen wrote, “I'm not sure if anyone else is looking into 2023 JN16, but it's very bright to have been missed all this time and just now be discovered in 2023. It should be brighter than magnitude 22 every day of the year for many decades (regularly reaching magnitude 18) and was only just discovered. I think there's a real chance it's active or in outburst.”

 

In response to Peter’s post, observers identified a cometary activity in images taken between June 2023 and June 2024. Interestingly, the ZTF survey reported that the object was detected in images taken on 2023 April 29 but not in images taken on April 27 or earlier, suggesting an outburst, impact, or break-up event between those dates.

 

The object is on a typical Main Belt orbit with an orbital period of 4.4 years, perihelion at 2.30 au, semi-major axis of 2.70 au, and inclination of 3.7 degrees. [CBET 5430, MPEC 2024-Q04]

 

Comets Brighter than Magnitude 6

 

C/2023 A3 (Tsuchinshan-ATLAS)

 

Discovered on 2023 January 9 at the Purple Mountain Observatory's XuYi Station and on February 22 by ATLAS
Dynamically new long-period comet

 

Orbit (from Minor Planet Center, MPEC 2024-P125)

 

    C/2023 A3 (Tsuchinshan-ATLAS)                                              
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5                                        
T 2024 Sept. 27.74083 TT                                Rudenko                
q   0.3914103            (2000.0)            P               Q                 
z  -0.0002358      Peri.  308.49352     +0.36145497     +0.90082653            
 +/-0.0000004      Node    21.55948     +0.91852494     -0.29970120            
e   1.0000923      Incl.  139.11044     -0.16019439     +0.31415084            
From 4947 observations 2022 Apr. 9-2024 Aug. 2, mean residual 0".4.            
1/a(orig) = +0.000005 AU**-1, 1/a(fut) = -0.000036 AU**-1.

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2023 A3 (Tsuchinshan-ATLAS)                                                 Max El
                                                                               (deg)
                                                                         Ast Twi   Nau Twi
    Date      R.A.   Decl.     r       d    Elong  Ph.Ang.  Const  Mag  40N  40S  40N  40S
2024-Sep-01  10 43  -03 17   0.781   1.743    11E     15     Sext  6.5  -25   -9  -19   -3
2024-Sep-06  10 41  -04 01   0.684   1.642    11M     17     Sext  6.0  -21   -7  -15   -1
2024-Sep-11  10 38  -04 44   0.589   1.519    13M     23     Sext  5.5  -17   -4  -10    2
2024-Sep-16  10 36  -05 24   0.502   1.370    16M     35     Sext  5.0  -12   -1   -5    5
2024-Sep-21  10 35  -05 55   0.432   1.191    20M     54     Sext  4.3   -7    1   -1    7
2024-Sep-26  10 42  -06 06   0.394   0.983    22M     81     Sext  3.4   -4    2    2    8
2024-Oct-01  11 04  -05 44   0.402   0.767    21M    114     Leo   2.2   -4   -1    2    5
2024-Oct-06  11 57  -04 31   0.451   0.581    12M    150     Vir  -0.2   -9  -10   -3   -4

 

Comet Magnitude Formula (from ALPO, COBS, and MPC data)

 

m1 = -16.6 + 5 log d + 35.0 log r [Through T-650 days]
m1 =   0.2 + 5 log d + 15.7 log r [Between T-650 and T-300 days]
m1 =   6.0 + 5 log d +  6.6 log r [Between T-300 days and perihelion]
m1 =   7.4 + 5 log d + 10.0 log r [After perihelion, assumed]
where “t” is the date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au

 

C2023A3_LC_202409.jpg

 

Like with Mark Twain, the reports of C/2023 A3 (Tsuchinshan-ATLAS)’s demise have been greatly exaggerated. At least until August 21, when the last observations were made, Tsuchinshan-ATLAS was still going strong.

 

Most northern hemisphere observers lost sight of the comet in July, while southern hemisphere observations continued through August 12. The STEREO-A spacecraft also observed the comet between August 1 and 21.

 

So, for now, the comet looks healthy and displays a dust and gas tail. The following predictions assume it will continue to brighten at its recent rate, a relatively slow 6.6 log r. We will also assume that it will survive perihelion, which is always a question mark for dynamically new comets (assuming that the comet is dynamically new).

 

September sees Tsuchinshan-ATLAS start the month at a small solar elongation of 11 degrees, 0.78 au from the Sun, and 1.74 au from Earth. On the 27th, it arrives at perihelion at 0.39 au from the Sun, 0.91 au from Earth, but a solar elongation of 23 degrees.

 

The following table expands on the one above and shows the comet's altitude at the start of astronomical and nautical twilight in the morning sky from +40 and -40 degrees latitude. It highlights how difficult it will be to observe Tsuchinshan-ATLAS in September, especially from the northern hemisphere. One will need a clear sky with a flat, unobstructed morning eastern horizon. The magnitude predictions include enhanced brightness due to the forward scattering of dust at large-phase angles.

 

                           Max El
                            (deg)
                    40S               40N
    Date     Nau Twi  Ast Twi  Nau Twi  Ast Twi   r    delta  Elong  Ph.Ang.  Mag
2024-Sep-09     1                                0.63   1.57    12      20    5.7
2024-Sep-10     1                                0.61   1.55    12      21    5.6
2024-Sep-11     2                                0.59   1.52    13      23    5.5
2024-Sep-12     2                                0.57   1.49    14      25    5.4
2024-Sep-13     3                                0.55   1.46    14      27    5.3
2024-Sep-14     4                                0.54   1.43    15      30    5.2
2024-Sep-15     4                                0.52   1.40    16      32    5.1
2024-Sep-16     5                                0.50   1.37    16      35    5.0
2024-Sep-17     5                                0.49   1.34    17      38    4.8
2024-Sep-18     6                                0.47   1.30    18      42    4.7
2024-Sep-19     6                                0.46   1.27    19      46    4.6
2024-Sep-20     7       1                        0.44   1.23    19      50    4.5
2024-Sep-21     7       1                        0.43   1.19    20      54    4.3
2024-Sep-22     7       1                        0.42   1.15    21      59    4.2
2024-Sep-23     8       2                        0.41   1.11    21      64    4.0
2024-Sep-24     8       2         1              0.41   1.07    22      69    3.8
2024-Sep-25     8       2         2              0.40   1.03    22      75    3.6
2024-Sep-26     8       2         2              0.39   0.98    22      81    3.4
2024-Sep-27     8       2         2              0.39   0.94    22      87    3.2
2024-Sep-28     7       1         3              0.39   0.90    22      93    3.0
2024-Sep-29     7       1         3              0.39   0.85    22     100    2.7
2024-Sep-30     6                 3              0.40   0.81    22     107    2.5
2024-Oct-01     5                 2              0.40   0.77    21     114    2.2
2024-Oct-02     4                 2              0.41   0.73    20     121    1.9
2024-Oct-03     2                 1              0.42   0.69    19     128    1.5
2024-Oct-04     1                                0.43   0.65    17     135    1.0

 

September 1 [0.78 au from the Sun, 1.74 au from Earth, 11 deg solar elongation, 15 deg phase angle]
Tsuchinshan-ATLAS is at magnitude 6.5 but too faint and close to the Sun to be observed from the ground.

 

September 14 [0.54 au from the Sun, 1.43 au from Earth, 15 deg solar elongation, 30 deg phase angle]
Tsuchinshan-ATLAS may be as bright as magnitude 5.2. Imagers in the southern hemisphere may be able to image the comet during nautical twilight in the morning. It is probably still too faint and close to the Sun for visual observation.

 

September 20 [0.44 au from the Sun, 1.23 au from Earth, 19 deg solar elongation, 50 deg phase angle]
The comet rises at the start of morning astronomical twilight from mid-latitudes in the southern hemisphere. At magnitude 4.5, it should be visually observable for those with a clear, flat horizon. It won’t rise until well into nautical twilight for observers at northern mid-latitudes.

 

September 25 [0.40 au from the Sun, 1.03 au from Earth, 22 deg solar elongation, 75 deg phase angle]
Tsuchinshan-ATLAS is at its highest in the morning sky for southern mid-latitude observers. Still, “highest” means it will only be 2 degrees above the horizon at the start of astronomical twilight and 8 degrees at the start of nautical twilight. The comet should be around magnitude 3.6.

 

September 27 [0.39 au from the Sun, 0.94 au from Earth, 22 deg solar elongation, 87 deg phase angle]
Tsuchinshan-ATLAS is at perihelion and magnitude 3.2. Conditions from the southern hemisphere are similar to those on the 20th. The comet should be bright enough to be imaged from the northern hemisphere, but visual observations may still not be possible.

 

September 29 [0.39 au from the Sun, 0.85 au from Earth, 22 deg solar elongation, 100 deg phase angle]
Tsuchinshan-ATLAS is at its highest in the morning sky for northern mid-latitude observers. Still, it doesn’t rise before the start of twilight and is only 3 degrees at the start of nautical twilight. Tsuchinshan-ATLAS is around magnitude 2.7. Though now past perihelion, the comet is rapidly brightening due to a decreasing Earth-comet distance and increasing phase angle. In the next few days, we will see observability as a contest between a lower altitude and brighter sky, but also a brighter comet.

 

Comets Between Magnitude 6 and 10

 

13P/Olbers

 

Discovered visually on 1815 March 6 by Heinrich Olbers in Bremen, Germany
Halley-type comet

 

Orbit (from Minor Planet Center, MPEC 2024-Q42)

 

  13P/Olbers                                                                   
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5                                        
T 2024 June 30.04994 TT                                 Rudenko                
q   1.1754681            (2000.0)            P               Q                 
n   0.01423818     Peri.   64.41676     -0.60853213     -0.37163125            
a  16.8590520      Node    85.84708     +0.18555929     -0.92570126            
e   0.9302767      Incl.   44.66599     +0.77152861     -0.07047968            
P  69.2                                                                        
From 1876 observations 2023 Oct. 8-2024 Aug. 25, mean residual 0".5.           
     Nongravitational parameters A1 = +0.65, A2 = -0.3232.                     

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

13P/Olbers                                                      Max El
                                                                 (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag  40N  40S
2024-Sep-01  13 18  +18 49   1.505   2.140    39E   Com   8.2   18    5
2024-Sep-06  13 34  +16 15   1.550   2.198    38E   Com   8.4   18    5
2024-Sep-11  13 48  +13 45   1.597   2.260    38E   Boo   8.7   17    5
2024-Sep-16  14 02  +11 22   1.645   2.326    37E   Boo   9.0   16    5
2024-Sep-21  14 15  +09 06   1.694   2.395    36E   Boo   9.3   15    4
2024-Sep-26  14 28  +06 56   1.743   2.467    35E   Vir   9.5   14    3
2024-Oct-01  14 40  +04 54   1.794   2.541    33E   Vir   9.8   13    2
2024-Oct-06  14 51  +02 59   1.845   2.616    31E   Vir  10.1   12    1

 

Comet Magnitude Formula (from 1956 ICQ and 2023 ALPO data)

 

m1 = -0.9 + 5 log d + 32.9 log r [Up through T-120 days]
m1 =  3.9 + 5 log d + 16.6 log r (T – 8)[After T-120 days]
where “T” is date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au

 

13P_LC_202409.jpg

 

13P/Olbers is one of two returning Halley-type comets expected to be brighter than magnitude 12 this month. Last at perihelion in 1956, this year’s return saw perihelion on 2024 June 30 at 1.18 au and a peak brightness of magnitude 6.5 reached in July.

 

September sees Olbers as a low evening object, especially from the southern hemisphere, as it moves through Coma Berenices (Sep 1-6), Boötes (6-24), and Virgo (24-30). Since it is past perihelion, its distance from the Sun and Earth is increasing, resulting in a steady fade from around magnitude 8.2 on the 1st to 9.8 at the end of the month.

 

Photo Opportunities
Sep 01 - 13P/Olbers within a degree or so of the bright globular cluster pair M53 and NGC 5053
Sep 30 - 13P/Olbers passes within 20’ of 10th mag galaxy NGC 5701

 

Comets Between Magnitude 10 and 12

 

12P/Pons-Brooks

 

Discovered visually on 1812 July 12 by Jean-Louis Pons and rediscovered visually on 1883 September 2 by William R. Brooks
Halley-type comet

 

Orbit (from Minor Planet Center, MPEC 2024-Q42)

 

  12P/Pons-Brooks                                                              
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5                                        
T 2024 Apr. 21.12533 TT                                 Rudenko                
q   0.7808584            (2000.0)            P               Q                 
n   0.01381092     Peri.  198.99348     +0.14509852     -0.32930545            
a  17.2049860      Node   255.85512     +0.98567050     +0.13009697            
e   0.9546144      Incl.   74.19215     +0.08602381     -0.93521800            
P  71.4                                                                        
From 1242 observations 2024 Feb. 1-Aug. 21, mean residual 0".6.                

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

12P/Pons-Brooks                                                 Max El
                                                                 (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag  40N  40S
2024-Sep-01  12 20  -47 23   2.274   2.607    59E   Cen  10.5    0   34
2024-Sep-06  12 36  -47 28   2.337   2.708    58E   Cen  10.7    0   33
2024-Sep-11  12 52  -47 30   2.398   2.810    56E   Cen  10.9    0   31
2024-Sep-16  13 06  -47 32   2.459   2.912    53E   Cen  11.0    0   30
2024-Sep-21  13 20  -47 32   2.520   3.014    51E   Cen  11.2    0   28
2024-Sep-26  13 33  -47 32   2.580   3.114    49E   Cen  11.4    0   26
2024-Oct-01  13 46  -47 32   2.640   3.214    47E   Cen  11.6    0   24
2024-Oct-06  13 58  -47 32   2.700   3.311    45E   Cen  11.7    0   23

 

Comet Magnitude Formula (from ALPO and COBS data for the 1954 and 2023 returns)

 

m1 =  6.8 + 5 log d + 11.6 log r [between T-684 and T-275 days]
m1 =  4.2 + 5 log d +  9.7 log r [between T-275 days and perihelion]
m1 =  4.7 + 5 log d + 10.3 log r [after perihelion]
where “t” is date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au

 

12P_LC_202409.jpg

 

The other returning Halley-type comet is 12P/Pons-Brooks, which is four months from its perihelion in late April at 0.78 au from the Sun. As September begins, the comet has already receded to a distance of 2.3 au from the Sun and 2.6 au from Earth.

 

This month, Halley-type comet 12P/Pons-Brooks fades from around magnitude 10.5 to 11.6. The comet is making its first return since 1954. Now past its April perihelion at 0.78 au, Pons-Brooks is receding back into the outer solar system. Its next perihelion will be in 71 years, in 2095.

 

The comet continues to be a southern-hemisphere-only object in Centaurus. Its path through Centaurus will provide one of the viewing/imaging highlights of the month as Pons-Brooks passes over the magnificent and bright globular cluster Omega Centauri (NGC 5139) on September 22-23.


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#2 Octans

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Posted 10 September 2024 - 03:58 PM

The Hayabusa2 team just posted this clip of C/2023 A3 continuing to steadily brighten over the last couple weeks: https://x.com/haya2_...448389310353616


Edited by Octans, 10 September 2024 - 04:00 PM.


#3 Octans

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Posted 11 September 2024 - 10:27 PM

And an image from the ground by Terry Lovejoy at around mag 5.5: https://www.facebook...89996839028496/

Using a dedicated high phase angle (>160 deg) scattering model, the peak brightness on October 9 (173 deg) is looking like it'll be near mag -5 to -6.


Edited by Octans, 11 September 2024 - 10:29 PM.

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#4 BrooksObs

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Posted 12 September 2024 - 03:29 PM

Most unfortunately, c/2023 A3 greatly enhance brightness phase will be quite limited, generally lasting only a few days. As the comet's elongation from the Sun increases its total magnitude will be rapidly decreasing in step, such that observers will need to start searching for the comet ASAP after October 10-11 to pick it up and likewise to find a viewing location with a very low, unobstructed, western horizon to gain the earliest and best views.

 

As it looks right now, I anticipate the comet to attain about the brightness of Venus when at her maximum. Unfortunately, Venus will be far removed in the sky as a comparison object. Although much better situated, Mercury will be difficult to detect very closely southeast of the Sun. Only those observers of great experience in near-sun observation might be likely to safely pick-up the comet on October 9-10, but individuals exercising considerable caution a day or 2 before and particularly after these days may be successful at spotting the comet in  full daylight around local noon but only in very clear blue skies.

 

But other visually striking phenomenon might also be presented beyond simply great brightness. In the days immediately following the comet's peak brightness the Earth will be crossing through the orbital plane of the comet. Given the apparent level of dust density exhibited in images of the type II tail pre-T and dependent on the tail's degree of curve, not only will a brilliant, spike-like anomalous tail become briefly visible pointing sunward for a few days, but a wave of light could appear to move down its sunward pointing shaft as the effects of forward scattering once again come into play!

 

BrooksObs


Edited by BrooksObs, 12 September 2024 - 03:42 PM.

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#5 Carl H.

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Posted 12 September 2024 - 07:26 PM

And images of C/2023 A3 from Michael Mattiazzo: https://groups.io/g/...l/message/32553

 

Terry estimated a brightness of magnitude 5.5 and Michael of 5.2. Both are close to our brightness prediction.

 

Can't wait to see it from the northern hemisphere. Hopefully, the smoke will subside by then.


Edited by Carl H., 12 September 2024 - 07:38 PM.


#6 Octans

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Posted 13 September 2024 - 12:06 AM

One other interesting aspect of this comet is that Earth will likely cross through its ion tail around October 11-12 UT, assuming typical solar wind conditions (~400 km/s). With the nucleus quite distant at ~0.5 au away, this will almost certainly *not* be a particularly spectacular event, and might not be observable at all by anything but solar wind monitoring spacecraft. However, there's a chance a very large (both long and wide) but extremely tenuous ion tail could be spotted around this period under very dark skies while the head of the comet (still very close to the Sun) is well below the horizon.


Edited by Octans, 13 September 2024 - 12:09 AM.


#7 Carl H.

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Posted 13 September 2024 - 12:24 PM

One other interesting aspect of this comet is that Earth will likely cross through its ion tail around October 11-12 UT, assuming typical solar wind conditions (~400 km/s). With the nucleus quite distant at ~0.5 au away, this will almost certainly *not* be a particularly spectacular event, and might not be observable at all by anything but solar wind monitoring spacecraft. However, there's a chance a very large (both long and wide) but extremely tenuous ion tail could be spotted around this period under very dark skies while the head of the comet (still very close to the Sun) is well below the horizon.

Unfortunately the Moon will be between 1Q and Full at that time. For Oct 11-12 UT, it's percent illumination will be around 70%. The Moon will hinder observations of A3 until it leaves the evening sky after Oct. 20 UT.



#8 Octans

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Posted 13 September 2024 - 01:16 PM

Unfortunately the Moon will be between 1Q and Full at that time. For Oct 11-12 UT, it's percent illumination will be around 70%. The Moon will hinder observations of A3 until it leaves the evening sky after Oct. 20 UT.

It's certainly not optimal, but the best viewing (which might still be nothing) would probably be on the morning side just prior to the ion tail crossing on the 11th when the Moon is down. Earth will be ~4 degrees south of the antisunward line, so the bulk of the ion tail will probably be off to the north, though exact direction/timing depends on the exact solar wind conditions (which can cause ion tails to swing by more than the ~4 degree nominal offset). If anything ends up observable at all, it would probably be by an all sky camera (or at least wide field cameras covering a large fraction of sky).

 

Another unusual and also tenuous feature to look out for is the dust antitail stretching past the Sun into the morning sky while the head of the comet is well into the evening sky, similar to how C/McNaught's tail remained visible in the Northern Hemisphere well after the comet itself moved far south. The tail would probably have to extend >50 degrees for this observation (25 degrees to the Sun + >25 degrees beyond). However, with the favorable plane crossing geometry compressing the dust into a sharp line and putting the dust at higher phase angle/closer to Earth than the nucleus at the same elongation, and the Moon being down during the optimal observing window, it might be possible.



#9 Octans

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Posted 15 September 2024 - 04:42 AM

So now for a bit of bad news in regards to daylight visibility: After spending some time making a more accurate surface brightness model based currently on eyeball estimates of size of the coma from the several recently posted images, I no longer expect it to be visible to the naked eye in daylight, and the comet will likely be a tough visual target even telescopically.

 

The key problem here is the coma will be very large compared to C/McNaught, most likely ~10-15' in diameter, due to a combination of the comet being fairly close to Earth (0.5 au), and the contribution of the physical tail projected along the line of sight to the apparent coma at the high phase angle. Astronauts in space who can see the full extent of the coma and tail against a dark background (and care to look) should still see a comet in the magnitude -5 to -6 range, and very deep exposures sensitive to details well below daylight sky brightness may find something similar. However, ground-based visual observers even under the best conditions on Earth are unlikely to see anything remotely close to that brightness, with the innermost ~30" of the coma likely being only around magnitude -2. For comparison, Venus on the same day will be magnitude -4 at only 13" diameter. To be clear, because the dust coma is centrally condensed, the very center of the coma should still be visible through a small telescope under decent sky conditions, but it won't be anywhere close to as obvious as the much more compact C/McNaught was.

 

I'll post some graphics later near perihelion once the details have settled down.


Edited by Octans, 15 September 2024 - 05:22 AM.


#10 Carl H.

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Posted 22 September 2024 - 12:40 PM

This morning, I made my first attempt to observe C/2023 A3 (Tsuchinshan-ATLAS) from Tucson (lat 32N). I'm happy to report that it was successful.

 

2023A3  2024 09 22.52 aI  3.9:TK  5.0B    10   1.5  7            ICQ XX HER02 Carl Hergenrother

 

The comet was picked up at an elevation of ~3 deg after rising above the horizon from my house. The comet was first seen around 12:22 UT, but only followed till 12:25 UT before the sky became too bright. At the time, the Sun was ~11 degrees below the horizon.

 

Using the ICQ's average extinction table, I estimated a magnitude of 3.9. In 10x50s, the comet was highly condensed with a hint (averted imagination) of a tail.


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#11 Carl H.

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Posted 24 September 2024 - 06:09 PM

Two more observations of C/2023 A3 from Tucson.

 

   2023A3  2024 09 24.51 aS  3.5:TK  5.0B    10   1.5  7   0.5  250 ICQ XX HER02 Carl Hergenrother
   2023A3  2024 09 23.51 aS  3.5:TK  5.0B    10   2    7   0.5  250 ICQ XX HER02 Carl Hergenrother

 

This morning (Sep. 24.51), I was able to follow the comet till 12:35 UT when the Sun was only 8 deg below the horizon. 



#12 Carl H.

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Posted 24 September 2024 - 06:11 PM

Here's a plot showing the elevation of the comet at the start of nautical twilight when the Sun is 12 degrees below the horizon, as well as for the end of nautical twilight when the comet is in the evening sky in a few weeks. There are elevation curves for latitudes of -50, -30, 0, +30, +40, +50, and +60.

 

C2023A3_elevation.jpg


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#13 emh52

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Posted 25 September 2024 - 11:30 AM

What is left of 12P Pons-Brooks and the photo op.  The comet was nearly invisible as it passed over the cluster but now with some separation a faint but obvious tail is visible as well as a coma surrounding the nucleus. Not much time left to observe it is low in the sky in Chile and will be out of range  very soon.

 

https://flic.kr/p/2qiE2mp

 

Attached Thumbnails

  • cn 12P 92424.jpg

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#14 Carl H.

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Posted 26 September 2024 - 12:43 PM

We are now 1 day from perihelion. This morning (Sep 26.51), I estimated the comet at magnitude 3.0. 

 

I tried to observe it yesterday morning (Sep 25.51 UT). While I was successful in observing the comet, there was so much forest fire smoke in the direction of the comet that I didn't bother with a magnitude estimate.

 

   2023A3  2024 09 26.51 aM  3.0 TK  5.0B    10   1.5  7   0.5  250 ICQ XX HER02 Carl Hergenrother



#15 Carl H.

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Posted 02 October 2024 - 02:08 PM

I am still working on the October ALPO Comet News thanks to C/2024 S1 (ATLAS). In the meantime, the clear weather (mostly) continues here in Tucson. Here are my C/2023 A3 observations from the past few mornings.

 

   2023A3  2024 10 02.52 aI  1.2 TK  0.0E     1   3    9   1    260 ICQ XX HER02 Carl Hergenrother
   2023A3  2024 10 02.52 aM  1.5 TK  5.0B    10   2    8   2.5  260 ICQ XX HER02 Carl Hergenrother
   2023A3  2024 09 30.51 aM  2.1 TK  5.0B    10   2    7/  2    250 ICQ XX HER02 Carl Hergenrother
   2023A3  2024 09 28.51 aM  2.5 TK  5.0B    10   2    7   1    250 ICQ XX HER02 Carl Hergenrother
   2023A3  2024 09 27.51 aM  2.8 TK  5.0B    10   2    7   1    250 ICQ XX HER02 Carl Hergenrother

 

The comet is now a naked eye object with a naked eye tail.

 

The window to observe the comet in the morning sky is rapidly closing. I'm sure it will be observable tomorrow morning and possibly the two mornings after that.



#16 Carl H.

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Posted 04 October 2024 - 06:52 PM

The October ALPO Comet News is up at https://www.cloudyni...r-october-2024/ .


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